RNA interference (RNAi) or gene silencing involves the use of double
stranded RNA (dsRNA). Once inside the cell, this material is processed
into short 21-23 nucleotide RNAs termed siRNAs that are used in a
sequence-specific manner to recognize and destroy complementary RNA. The
report compares RNAi with other antisense approaches using
oligonucleotides, aptamers, ribozymes, peptide nucleic acid and locked
nucleic acid.

Various RNAi technologies are described, along with design and methods
of manufacture of siRNA reagents. These include chemical synthesis by in
vitro transcription and use of plasmid or viral vectors. Other
approaches to RNAi include DNA-directed RNAi (ddRNAi) that is used to
produce dsRNA inside the cell, which is cleaved into siRNA by the action
of Dicer, a specific type of RNAse III. MicroRNAs are derived by
processing of short hairpins that can inhibit the mRNAs. Expressed
interfering RNA (eiRNA) is used to express dsRNA intracellularly from
DNA plasmids.

Delivery of therapeutics to the target tissues is an important
consideration. siRNAs can be delivered to cells in culture by
electroporation or by transfection using plasmid or viral vectors. In
vivo delivery of siRNAs can be carried out by injection into tissues or
blood vessels or use of synthetic and viral vectors.

Because of its ability to silence any gne once the sequence is known,
RNAi has been adopted as the research tool to discriminate gene
function. After the genome of an organism is sequenced, RNAi can be
designed to target every gene in the genome and target for specific
phenotypes. Several methods of gene expression analysis are available
and there is still need for sensitive methods of detection of gene
expression as a baseline and measurement after gene silencing. RNAi
microarray has been devised and can be tailored to meet the needs for
high throughput screens for identifying appropriate RNAi probes. RNAi is
an important method for analyzing gene function and identifying new drug
targets that uses double-stranded RNA to knock down or silence specific
genes. With the advent of vector-mediated siRNA delivery methods it is
now possible to make transgenic animals that can silence gene expression
stably. These technologies point to the usefulness of RNAi for drug
discovery.

RNAi can be rationally designed to block the expression of any target
gene, including genes for which traditional small molecule inhibitors
cannot be found. Areas of therapeutic applications include virus
infections, cancer, genetic disorders and neurological diseases.
Research at academic centers that is relevant to RNAi-based therapeutics
is mentioned.

Regulatory, safety and patent issues are discussed. Side effects can
result from unintended interaction between an siRNA compound and an
unrelated host gene. If RNAi compounds are designed poorly, there is an
increased chance for non-specific interaction with host genes that may
cause adverse effects in the host. However, there are no major safety
concerns and regulations are in preliminary stages as the clinical
trials are still ongoing and there are no marketed products. Many of the
patents are still pending.

The markets for RNAi are difficult to define as no RNAi-based product is
approved yet but several are in clinical trials. The major use of RNAi
reagents is in research but it partially overlaps that of drug discovery
and therapeutic development. Various markets relevant to RNAi are
analyzed from 2013 to 2023. Markets are also analyzed according to
technologies and use of siRNAs, miRNAs, etc.

Profiles of 161 companies involved in developing RNAi technologies are
presented along with 233 collaborations. They are a mix of companies
that supply reagents and technologies (nearly half of all) and companies
that use the technologies for drug discovery. Out of these, 33 are
developing RNAi-based therapeutics and 35 are involved in microRNAs. The
bibliography contains selected 600 publications that are cited in the
report. The text is supplemented with 37 tables and 11 figures.